Cell culture studies allow air pollution researchers to assess toxicological outcomes that can be later used in human exposure models and risk assessment studies. However, there are only a few collection systems that allow direct cellular exposure to ambient pollutants. All these systems, due to their large size and complexity, are laboratory devices and cannot be deployed easily for field studies. In this project we propose a new approach for a more direct and faster assessment of in-vitro toxicity of airborne particulate matter (PM). The main objective is to develop a new sampling system that allows direct, real-time exposure of cells to PM, which reduces the extent of sampling artifacts as well as sample manipulation prior to cell exposure. The advantage of this new system compared with the existing ones is that it uses water-based particle growth for efficient collection and deposition o particles with aerodynamic diameters ranging from 5 nm to 5 ?m. This technology also avoids the most common problem associated with other particle collection systems, the possibility of changing the physical, chemical and toxicological properties of the particles prior to cell exposure. In addition, its small size and low power requirements make the device suitable for both laboratory work and field deployment. The approach offers a new alternative for direct cellular exposure studies. It provides more accurate results when studying cellular responses to PM exposure and thus a better understanding of the possible adverse outcomes related with exposure to ambient pollutants. Our goal will be achieved by completing the following specific aims: i) adapt the existing collection chamber to maintain environmental conditions suitable for viable and healthy cells; and ii) conduct laboratory controlled exposure studies to evaluate whether our approach leads to identifiable biological responses and cell toxicity. In summary, our device brings together a well established technology with innovative applications, providing the means to expose cells directly to airborne particles, and to measure more accurately metabolic responses associated with exposure to airborne PM.